1. Field of the Invention
The present invention relates to an anode used for corrosion protection of a reinforcing steel covered with a concrete layer, a corrosion-protecting structure of a concrete constructions using the same and a corrosion protection method of the concrete constructions.
2. Description of the Conventional Art
There has been known an electric corrosion protection which lowers an electric potential of a steel product to a corrosion-free electric potential by applying an electric current to the steel product such as a reinforcing steel in a concrete from an electrode (an anode) which is installed in the vicinity of a surface of the concrete, thereby suppressing progress of the corrosion of the steel product. An impressed current system and a galvanic anode have been known as the electric corrosion protection.
The impressed current system is a cathode corrosion protection in which an electric circuit is produced by connecting a positive pole of a DC power supply device to a steel product corrosion protecting an anode and a negative pole by an electric conductor, and a corrosion protection current is applied to the steel product from the anode.
The galvanic anode system is structured such that a galvanic anode (a sacrificial anode) is connected to the steel product by the electric conductor, the galvanic anode being made of a material having a lower oxidation-reduction potential than the steel product to be electrically corrosion protected, for example, a base metal such as zinc, magnesium or aluminum or alloys thereof, and the metal of the galvanic anode is ionized in place of the steel product so as to prevent corrosion of the steel product. In other words, the galvanic anode system is a method of completing an electric battery by using the corrosion protecting steel product as the cathode and using a material having a lower oxidation-reduction potential than the steel product as the anode, and flowing a corrosion protection current to the steel product on the basis of difference in potential between both the electrodes.
However, since the galvanic anode system depletes the material having the low oxidation-reduction potential with age, the galvanic anode system has such a problem that it is necessary to periodically change the galvanic anode.
On the other hand, since the impressed current system is structured such that the anode having a high corrosion resistance such as a titanium mesh, a titanium grid or a titanium rod is installed to a surface of the concrete or installed by forming a groove or a hole on the surface, and is fixed by a mortar, it is not necessary to periodically change the anode, however, there is such a problem that the anode having the high corrosion resistance is expensive and is disadvantageous in cost, and it takes a lot of trouble with construction.
Further, there is a method of attaching platinum titanium wires to a concrete surface at intervals, and coating a whole surface of the concrete with a conductive coating material, however, since an electric potential distribution of a contact surface between a conductive coating film and the concrete is not uniform, there is such a problem that the conductive coating film is deteriorated by an electrochemical reaction and tends to be peeled.
With regard to the problems mentioned above, in recent years, there has been proposed a corrosion protection method utilizing a carbon fiber or a carbon powder while paying attention to the carbon fiber which is used for reinforcing at the time of repairing the concrete constructions.
For example, patent document 1 proposes an electric corrosion protection method of a reinforced concrete, the method attaching a material having a specific air permeability which is hard to pass salt content and water content to an inner side, attaching a sheet coated with a nonwoven fabric of a carbon fiber or a carbon powder to an inner side thereof, further attaching a protection cover coated with a non-shrink mortar in an inner side thereof to the outside of the reinforced concrete constructions, connecting a metal having a high corrosion resistance and the sheet in an end portion of the protection cover so as to form a current-carrying point in an anode side, forming a hole in the concrete at an appropriate position, and connecting the metal to the reinforcing steel so as to form a current-carrying point in a cathode side.
Further, patent document 2 proposes a corrosion protection method of attaching a carbon fiber sheet onto a surface of the existing concrete constructions including a steel product provided within the concrete, via a conductive adhesive agent, and applying an electric current so that the steel product is a cathode and the carbon fiber sheet is an anode.
Further, patent document 3 is proposed since it is hard to freely adjust a conductive property and an adhesion strength of the conductive adhesive agent in the proposal in the patent document 2, and proposes a corrosion protection method of applying an electric current so that a cathode is constructed by a steel product of a corrosion protection reinforced concrete assembly in which an adhesive agent layer for bonding a concrete constructions and a carbon fiber sheet is arranged so as to be sectioned from a layer of a conductive material having a higher conductive property than the adhesive agent, the adhesive agent layer and the steel product being arranged between a surface of the concrete constructions and the carbon fiber sheet, and an anode is constructed by the carbon fiber sheet.
Further, combination of a backfill is carried out as a means for assisting the proposals. For example, patent document 4 proposes a backfill for an electric corrosion protection of a concrete constructions which includes a water-absorbing resin and an alkaline aqueous solution and is in a gel state. According to the proposal, it is possible to prevent a liquid leakage of the backfill even in the case that the electric current is applied for a long time, an ionic conductive property and a water property are good, an excellent alkali buffer action is exhibited, and it is possible to apply such a service life property that an exciting performance is less reduced.